As previously underlined in this book, Pickering emulsions have in recent years gained increasing attention due to their interesting properties related to the replacement of surfactants by solid microparticles or nanoparticles. Such change in the nature of the stabilizer confers higher stability and lower toxicity to the emulsions. This chapter focuses on the recent advances in the specific use of a peculiar class of inorganic bidimensional particles, the Layered Double Hydroxides (LDH) and Layered Hydroxides Salts (LHS) in Pickering emulsion process. The properties of the two main classes of LDH involved in the stabilization of emulsion that is pristine materials and modified LDH with organic anions are described. Then the different results obtained for oil-in-water, water-in-oil, and water-in-water involving LDH or hydroxides salt particles are discussed. At last, the interest of Pickering emulsion stabilized by LDH in various applications is also reviewed.
The aim of this chapter is to propose a step-by-step approach for the study of emulsions stabilized by particles independently of the system chemical nature. This includes tools as simple as macroscopic observations of the obtained emulsions up to more sophisticated techniques, like electron microscopy or interfacial rheology. The progressive characterization allows collecting information at different length scales: at the level of the emulsion properties, at the level of drops, and down to the particle packing at the oil-water interface, highlighting the interaction between drops and adsorbed particles. The link between the various length scales is also enhanced. For example, bridging of particles adsorbed at the interface of neighboring drops is responsible for the adhesion between drops leading to a plug flow that can be assessed by naked eyes. Therefore, the chapter pretends to be a general guideline for studying a new unknown system, starting from scratch.
Clay minerals are abundant in the world, inexpensive, and have a wide range of structures and properties, besides being environmentally friendly and having mechanical/heat stability. They have complex structures composed of two-dimensional units called layers, separated or not by intercalated cations. The crystals can be delaminated and even exfoliated into single layers, and after proper chemical modifications, they can be applied in more sophisticated applications than at present. The objective of this chapter is to present the basic characteristics of clay minerals’ structures, properties, and the possible reactions involved, paying special attention to surface chemical modifications of micrometric bulk particles or single layers, to aggregate value and increase the applications of this fascinating class of materials.
This chapter describes the fundamental aspects of emulsion formation and of their stability, intended to provide a solid background for the reader to comprehend the more advanced concepts that will be presented over the next chapters. Emulsions are presented along their classical categorization regarding droplet size and type, including multiple emulsions. Physical–chemical aspects of macroemulsions formation are described, elucidating the origin of their thermodynamic instability, but also addressing the key aspects that may be used to ensure their kinetic stability. The physical mechanisms leading to their instability, such as creaming, sedimentation, flocculation, coalescence, and Ostwald ripening, are also explained. Finally, strategies on how to overcome this instability are illustrated, including high- and low-energy emulsification techniques, the parameters to guide the correct choice of emulsifiers, mostly the HLB concept, and other formulation aspects related to their electrostatic and steric stabilization, as well as the addition of rheology modifiers.
The clay mineral owing to the merit of cheap, abundant, non-toxic and varied morphology has been attracted increased interest in the preparation of Pickering emulsions or foams. Herein, this chapter summarizes the research progress of Pickering emulsions or foam stabilized with various clays, stabilization method, affect factors and its application. The clay minerals applied in Pickering emulsions or foams include the layered chain structured palygorskite (Pal) and sepiolite (Sep), tubular halloysite (Hal) as well as the layered structured montmorillonite (Mt), kaolinite (Kaol), Laponite (Lap), etc. The stabilization method contains the synergistic effect between clay minerals with organic small molecular, polymer and others particles with opposite charge. The influence factors including the size, shape and content of clay mineral, pH, salinity also is discussed and expatiated. In the last, the application of Pickering emulsion in enhanced oil recovery (EOR), heterogeneous catalysis, heritage conservation and construction of polymeric porous materials, polymeric nanoparticles (PNPs), etc., are summarized. To motivate further research of clay mineral-based Pickering emulsion or foam in fundamental research and practical applications, the outlook of existing challenges and opportunities for future development is also presented.
